Electronic organ key



C- W. M KEE ETAL ELECTRONIC ORGAN KEY Filed Dec. 16, 1959 United States Patent 3,125,738 ELECTRONIC ORGAN KEY Chester W. McKee, Flossmcor, Richard W. McKee, Lake Forest, and Charles M. Rich, Chicago, Ill., assignors to Welding Service, inc., Franklin Park, 111., a corporation of California Filed Dec. 16, 1959, Ser. No. 860,023 3 Claims. (Cl. 338-69) The present invention relates to a contact assembly for an electronic organ and more particularly to an improved contact assembly for an electronic organ which assembly incorporates isolating resistance.

In an electronic organ, when each key is depressed, a plurality of pairs of contacts are brought together or closed, each of which completes a circuit between a tone source and an output circuit. Ordinarily, one tone source is common to the contacts of more than one key. Consequently, the number of output circuits connected to the tone source, and thus the loading on the tone source, varies depending upon the number of contacts which are closed. If the pairs of contacts are connected directly to the tone source, there is a drastic change in the signal in eachoutput circuit as additional pairs of contacts are closed.

To minimize the variations in loading, in previously available electronic organs, a high ohmic isolating resistor has been connected in series with each pair of contacts. This has the disadvantage of adding extra parts to the electronic organ with the resultant increase in cost of manufacturing and maintenance.

An object of the present invention is the provision of a contact assembly which is provided with intrinsic isolating resistance. Another object of the present invention is the provision of an improved contact assembly for an electronic organ. Still another object is the provision of a contact assembly which is relatively inexpensive and simple to manufacture.

Other objects and advantages of the present invention will become apparent by reference to the following description and accompanying drawings.

In the drawings:

FIGURE 1 is a vertical, fragmentary cross-section of a contact assembly of an electronic organ showing various of the features of the present invention:

FIGURE 2 is a schematic perspective view of the contact assembly shown in FIGURE 1; and

FIGURE 3 is an enlarged cross-sectional View taken generally along line 3-3 of FIGURE 2.

Generally, a contact assembly in accordance with the present invention is provided with an intrinsic high ohmic series resistance. The contact assembly comprises at least one pair of contacts, each of which contacts is connected to an electronic circuit. Means are provided for moving the contacts relative to each other so that they contact each other at an area of contact on one of the contacts which is remote from the connection to the electronic circuit of that contact. The one contact includes a layer of insulating material and a second layer of a material having a high resistance per unit of length of the contact disposed on the first layer so as to connect the area of contact to the connection associated with the one contact.

More specifically, the contact assembly illustrated includes an elongated generally horizontally extending cylindrical contact or bus bar which is supported at both ends by suitable insulators 12. The insulators 12, in turn, are supported by a suitable frame 14 disposed in the electronic organ. One end of the bus bar 10 is connected by a conductor 16 to an output circuit (indicated diagrammatically at 18) of an electronic organ.

The bus bar 10 may be composed of a conductive material coated with a precious metal, such as gold, but pref- EJ253353 Patented Mar. 17, 1964 ice erably to reduce the cost of the manufacture, the bus bar it is coated with a conductive plastic, such as that described hereinafter.

Disposed at right angles to the bus bar 10 is a flexible, generally cylindrical and elongated contact 20. As illustrated, the contact 20 is supported in a horizontally extending position and in spaced relation to the bus bar 10 by a suitable insulator 22 connected at one end of the contact 20. The insulator 22, in turn, is mounted to the frame 14. The fixed end of the contact 20 is connected to a source of oscillation 24 by a conductor 26.

The free end of the contact 2% extends through an aperture 2.3 in an actuator 3th of insulating material. The actuator 39, which is employed to move the contact toward the bus bar W, is moved downwardly by pressing a key (not shown) on the keyboard of the electronic organ. As shown in FIGURE 1, the contact 20 touches the bus bar Ill at an area of contact 31 which is removed from the conductor 25. The contact 20 is composed of material having a high elasticity so that, when the actuator Tall is returned to its normal position by a spring or such (not shown), the contact Ztl recovers to its generally horizontally extending position.

Ordinarily, in an electronic organ contact assembly a plurality of bus bars are provided and a plurality of contacts are associated with each bus bar. For purposes of explanation only one bus bar and one of its associated contacts are described, but it should be understood that the other bus bars and contacts may be similarly constructed.

The contact 26 includes an elongated insulated and flexible central or body portion 32 which is covered with flexible coating 34 having a high resistance per unit length of the contact. (Resistance per unit length may be determined by measuring the DC. resistance of the coating from the area of contact to the connection and dividing it by the length between the area of contact and the con nection.) In this way, the resistance of the coating 34 is in series with the circuit between conductor 16 and conductor 26.

In the illustrated embodiment, the central portion 32 includes a wire 36 of a suitable elastic material such as spring steel which, since elastic material is ordinarily conductive, is covered with an insulating sleeve 38 of rubber, plastic, etc. The high resistance coating 34 is disposed on the sleeve 38.

The material employed for the coating 34 is of a resistivity such that the resistance from the area of contact with the bus bar to conductor 26 at the end of the contact 29 is suflicient to provide the required isolation resistance. A material suitable for use as a coating may be fabricated by dispersing particles of material having an appropriate conductivity over the sleeve 38 in such concentration as to produce the desired resistance per unit length of the contact. Higher concentration of the particles will decrease the resistance per unit length and lower concentrations will, of course, increase the resistance per unit length. The particles may be supported in any suitable manner.

Conductive particles may be dispersed in a relatively non-conductive plastic which may be fabricated into a coating 34 for the central portion 32 of the contact 20. In the plastic, conductive particles such as carbon, in the form of graphite or carbon black, metal particles, etc., may be used.

In one illustrative embodiment of the contact, a conductive plastic is made by mixing one part by weight of an aqueous emulsion containing 50 percent by weight of urea formaldehyde resin, a suitable emulsion being the one sold under the trade name of Formbond No. 436 by the Industrial Adhesive Co., and one part by weight of an aqueous emulsion containing 50 percent by weight of polyvinyl acetate such as that sold under the trade name Elvacet by Du Pont. Approximately 20 percent by weight of flaked graphite of a size which will pass through a 300 mesh screen is then added and throughly dispersed in the plastic emulsion. The resulting mixture is then diluted with sufficient water to provide the desired consistency and is then painted on a .030 inch diameter sleeve of extruded plastic which covers a .010 inch diameter spring steel Wire. The plastic carrier for the graphite is then cured. Suitable conditions for curing the plastic which has been described involve the use of a temperature of about 60 C., for two hours or drying it overnight at room temperature. The finished coating is about .010 inch in thickness and the resistance per inch of length is about 50,000 ohms.

As another illustrative embodiment of a coating of conductive plastic which may be used, one part by Weight of cellulose nitrate is mixed with two parts by weight of acetone. To this mixture about 1 percent by weight of acetyle tributyl citrate is added as a plasticizer. Approximately 20 percent by weight of flaked graphite of a size which will pass through a 300 mesh screen is added to the mixture and thoroughly dispersed therein. The graphite-plastic mixture is thinned, if necessary, with a suitable solvent, such as acetone, to produce the desired consistency, and is then applied to the insulating sleeve, of the contact in a similar manner as that described previously. The solvent is evaporated either by air drying or by the use of suitable drying equipment. The finished coating is about .010 inch in thickness and the resistance per inch of length of the contact is about 50,000 ohms per inch.

Depending upon the total resistance desired between the area of contact 31 and the conductor 26 connected at the end of the contact 20, the amount'of graphite, carbon black, or other material employed as the conductor can be varied over wide limits, the amount being limited only by the resistance per unit length desired and the mechanics of forming it into a coating of the desired thickness. Similarly, the thickness of the layer of material may be varied over wide limits, depending upon the resistivity of the material and the resistance per unit length desired. Other plastic carriers may also be used, including water emulsions, solutions of plastics or hot melt plastics, the only limitation upon the plastic being that it have a high resistance, i.e., that it is substantially an insulating material, and that it may be formed into the desired layer.

It should be understood that for a given resistance per unit length of the coating 34, the total resistance of the contact 20 may be increased by increasing the distance between the area of contact .31 with the bus bar and the conductor 26 connected to the source of oscillation 24. Also, for a given resistivity of coating material, the resistance per unit length may be increased by decreasing the thickness of the coating 34. For best results, the total resistance is approximately between 40 kilohms and 100 kilohms and, therefore, for a distance of 2 inches between the area of contact 31 and the conductor 26, the resistance per inch is approximately between 20,000 ohms per inch and 50,000 ohms per inch.

From the above it can be seen that the improved contact assembly minimizes loading on a tone source without the necessity of providing a separate isolating resistor. Moreover, conductive plastic employed on one or both of the contacts reduces the cost of the contact since a precious metal coating is not required.

Various changes may be made in the above described contact assembly without departing from the spirit or '4 scope of this invention. Various features of the invention are set forth in the accompanying claims.

We claim:

1. A contact assembly for an electronic organ comprising an elongated contact member supported only at one end, a first electronic circuit, means for selectively connecting said first electronic circuit to said contact member at a point spaced at a substantially fixed distance from said one end thereof, said contact member including means for providing a resistance between said connecting means and said one end, said resistance means including a coating on said contact member of synthetic, organic, non-elastomeric conductive plastic having a relatively high resistance per unit length and extending between said connecting means and said one end, and a second electronic circuit connected to said conductive plastic coating only at said one end whereby a predetermined resistance is provided between said point of contact and said second electronic circuit.

2. A contact assembly for an electronic organ comprising an elongated first contact member supported only at one end, a means for moving said first contact member, a first electronic circuit, a second contact member connected to said first electronic circuit and supported in the path of movement of said first contact member so that said first contact member is selectively pressed against said second contact member at a point of contact on said first contact member spaced at a substantially fixed distance from said one end of said first contact member, said first contact member including a layer of insulating material, and a layer of synthetic, organic, non-elastomeric conductive plastic having a relatively high resistance per unit length disposed on said insulating material, and a second electronic circuit connected to said conductive plastic layer only at said one end to provide a predetermined resistance between said point of contact and said second electronic circuit.

3. A contact assembly for an electronic organ comprising an elongated first contact member supported only at one end, means for moving said first contact member, a first electronic circuit, a second contact member connected tosaid first electronic circuit and supported in the path of movement of said first contact member so that said first contact member is selectively pressed against said second contact member at a point of contact on said first contact member spaced at a substantially fixed distance from said one end of said contact member, said first contact member including an elongated wire of spring material, a sleeve of insulating material on said wire, and a coating of synthetic, organic, non-elastomeric conductive plastic having a high resistance per unit length disposed on said sleeve and extending from the area of contact to said one end, and a second electronic circuit connected to said conductive plastic coating only at said one end whereby a predetermined resistance is provided between said area of contact and said second electronic circuit.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A CONTACT ASSEMBLY FOR AN ELECTRONIC ORGAN COMPRISING AN ELONGATED CONTACT MEMBER SUPPORTED ONLY AT ONE END, A FIRST ELECTRONIC CIRCUIT, MEANS FOR SELECTIVELY CONNECTING SAID FIRST ELECTRONIC CIRCUIT TO SAID CONTACT MEMBER AT A POINT SPACED AT A SUBSTANTIALLY FIXED DISTANCE FROM SAID ONE END THEREOF, SAID CONTACT MEMBER INCLUDING MEANS FOR PROVIDING A RESISTANCE BETWEEN SAID CONNECTING MEANS AND SAID ONE END, SAID RESISTANCE MEANS INCLUDING A COATING ON SAID CONTACT MEMBER OF SYNTHETIC, ORGANIC, NON-ELASTOMERIC CONDUCTIVBE PLASTIC HAVING A RELATIVELY HIGH RESISTANCE PER UNIT LENGTH AND EXTENDING BETWEEN SAID CONNECTING MEANS AND SAID ONE END, AND A SECOND ELECTRONIC CIRCUIT CONNECTED TO SAID CONDUCTIVE PLASTIC COATING ONLY AT SAID ONE END WHEREBY A PREDETERMINED RESISTANCE IS PROVIDED BETWEEN SAID POINT OF CONTACT AND SAID SECOND ELECTRONIC CIRCUIT. 